The techniques for carrying out superficial depositings of materials on substrates are well known and consist of evaporating or vaporizing a source which emits particles along a divergent beam in the direction of the substrate. Various methods to uniform the thickness of deposits have been proposed. For example, it is possible to place the substrates on the inner face of a dome-shaped support whose curvature center is close to the source. However, this solution can only be considered for simultaneously carrying out deposits on a large number of small substrates and not on extremely large flat substrates.
The technique closest approximating the method of the invention consists of making the substrate rotate around an axis parallel to the median emission direction of the beam, the axis being able to be possibly merged with this direction. The radial arm bears at its extremity the substrate whose outgoing normal line is either parallel to the axis or directed towards the latter. The surface to be covered in this case is turned towards the inside of the device. It is then advantageous to make the substrate itself rotate simultaneously at a speed of rotation normally clearly greater than the speed of rotation of the axis. In this way, a planet wheel motion of the substrate is embodied.
However, it is not possible to obtain deposits having thickness variations of less than 2% on large substrates (300 mm in diameter, for example). The chief objective of the invention is to obtain much better results.
The solution retained consists of inclining the substrate with respect to the axis of rotation so as to outwardly orientate its face receiving the deposit. Although this disposition may go against the previously described techniques of the prior art where an attempt is made to orientate the substrate in the direction of the source, it nevertheless considerably--and surprisingly--improves the uniformity of deposits.
Furthermore, the uniformity remains excellent as regards all the emissivity characteristics of the source: computer simulations have been conducted by making the coefficients of the expansion vary into a series of cosine powers .theta., a series whereby it is possible to characterize the intensity of radiation for any emission direction according to the angle .theta. it forms with the median emission direction of the beam. Extremely stable results have thus been obtained.